The extracellular matrix of animal connective tissues Flashcards
The classes of macromolecules that constitute the ECM are broadly similar, but it is the variation in their ___________and their _________ that give rise to diversity of tissues.
Relative amounts, organization
The ECM can become
can become calcified to become bone or teeth or it can become the transparent substance of the cornea or the rope-like organization of tendons
Matrix molecules are secretes by cells called
fibroblasts
In certain specialized connective tissues such as cartilage and bone, fibroblasts have specific names such as ________ and ________, respectively.
Chondrocytes, osteoblasts
The matrix in connective tissue is constructed from the same two main classes of macromolecules as in basal laminae:
1) glycosaminoglycan (GAG) polysaccharide chains usually covalently linked to proteins in the form of proteoglycans
2) fibrous proteins such as collagen.
Polysaccharides
resists compressive forces on the matrix while permitting rapid diffusion of nutrients, metabolites, and hormones between the blood and tissue cells
Collagen fibers
strengthen and help organize the matrix, while other fibrous proteins such as elastin (rubber-like) give it resilience.
Major protein of the extracellular matrix
Collagens
Collagens are secreted in large quantities by _______ and small quantities by _______
Connective tissue cells, many other cell types
What is the principal collagen of skin and bone
Type I collagen
After being secreted into the extracellular space, these collagen molecules assemble into higher order polymers called
collagen fibrils
Primary feature of a typical collagen molecule
its long, stiff, triple-stranded helical structure, in which three collagen polypeptide chains called α chains are wound around one another in a rope-like superhelix.
What are collagens extremely rich in that are found every 3rd a.a
Glycine
What does glycine allow for
allows the three helical α chains to pack tightly together to form the final collagen superhelix
What is found under the fibroblast cell
Long strands of collagen fibrils
Post-translational modifications collagen chains undergo
Individual collagen polypeptide chains are synthesized on membrane-bound ribosomes and injected into the lumen of the rough endoplasmic reticulum as large precursors called pro-α chains. After being trimmed, hydroxylated and glycosylated, each pro-α chain then combines with two others to form the triple-stranded, helical procollagen
________ and ________ are infrequently found in other animal proteins
Hydroxylysines and hydroxyprolines
What gives tissues their elasticity
Elastin
Vertebrate tissues need to be both ______ and ______
strong, elastic
What makes vertebrate tissue strong and elastic
Strong: collagen
Elastic: elastin
A network of elastic fibers in the ECM of these tissues
gives them the required __________- so that they can recoil after transient stretch.
Resilience
How is stretching and tearing limited
Long, non-elastic collagen fibrils are interwoven with elastic fibers
Like collagen, elastin is
unusually rich in proline and glycine
Unlike collagen, elastin is
not glycosylated and contains hydroxyproline but not hydroxylysine
The precursor of elastin
Soluble tropoelastin
How are elastic fibers assembled at the PM?
Soluble tropoelastin is secreted into the extracellular space and assembled into elastic fibers
What happens after secretion of tropoelastin
Tropoelastin becomes highly crosslinked to one another between lysines
The elastin protein is composed largely of WHAT two types of short segments that alternate along the polypeptide chain
1). hydrophobic segments which are responsible for the elastic properties
2 alanine- and lysine-rich alpha-helical segments which form cross-links between adjacent molecules
Fibronectin
an extracellular protein that helps cells attach to the matrix
The ECM contains a number of
non-collagen proteins with
binding sites for other matrix macromolecules and for cell-surface receptors
Fibronectin is found where an is important for
large glycoprotein found in all vertebrates and important for many cell-matrix interactions
What happens to mice that cant synthesize fibronectin
die early in embryogenesis because their endothelial cells are unable to form proper blood vessels.